Chlorofluorinated aromatic hydrocarbons are generally prepared by the Schiemann reaction or the fluorination of chlorinated aromatics with KF with or without a solvent. These methods are costly because of expensive reagents and relatively low yields.
Chlorofluorinated acyclic hydrocarbons are commercially prepared by reacting chlorinated hydrocarbons with hydrogen fluoride in the presence of a fluorination catalyst. In such HF reactions, for each mole of hydrogen fluoride reacted there is one mole of hydrogen chloride liberated. Because by-product hydrogen chloride does not have a steady market even after purification from small amounts of hydrogen fluoride contaminant, it is usually disposed of by dumping in rivers or in the ocean where permitted. The extra cost of this type of disposal is borne by the manufacturing operation. Furthermore, in view of environmental considerations, it is probable that such disposals will be restricted or eventually banned.
Recently, a new process has been developed for the production of chlorofluorinated aliphatic hydrocarbons which comprises reacting a mixture of a hydrocarbon and chlorine and hydrogen fluoride over a fluorination catalyst with a relatively large excess of recycled material consisting of underchlorinated and underfluorinated hydrocarbons. This process, which combines chlorination and fluorination in one step, however, produces more hydrogen chloride per unit weight of chlorofluorinated hydrocarbon than the standard commercial process referred to above. It thus intensifies rather than alleviates the hydrogen chloride by-product problem.
In view of the above discussion, it is apparent that there is a need in the industry for new technology for the manufacture of chlorofluorinated aromatic hydrocarbons which does not suffer from the hydrogen chloride by-product problem.
The oxychlorination of hydrocarbons by a Deacon type reaction is well known in the art. This involves the chlorination of an alkane or a chloroalkane with chlorine or hydrogen chloride in the presence of an oxygen-containing gas such as air, and in the presence of a Deacon-type catalyst such as a metal halide impregnated on a suitable carrier. It is postulated that in such an oxychlorination reaction, hydrogen chloride is oxidized to chlorine and water and the chlorine thus produced then reacts with the organic material. In this manner, by-product hydrogen chloride is eliminated or at least substantially minimized.
Vapor phase fluorination of chlorinated aliphatic hydrocarbons with and without the presence of a catalyst is also well known.
The combination of an oxychlorination reaction and a fluorination or chlorofluorination reaction into a simultaneous one-step oxychlorofluorination process is suggested in British Patent 745,818, published Mar. 7, 1956. Such a one-step process, if commercially feasible, would be of substantial value not only in the avoidance of the HCl problem but also in the potential savings in capital equipment and energy expenditure.
The British patent is restricted to aliphatic-compounds and, in any event, unfortunately, the process as described is not commercially practical. Attempts to duplicate the catalyst systems described in the British patent have been unsuccessful. The CuCl.sub.2 loading recommended in the patent exceeds the absorptive capacity of the carrier by more than two-fold. The excess CuCl.sub.2 loading has been found to create serious operating problems such as plugging, corrosion and erratic performance because of undue vaporization and run-off of the CuCl.sub.2. Another disadvantage found for such high CuCl.sub.2 loading is that it deactivates the fluorination sites on the carrier thus causing a significant decrease in HF conversions.
Others have experimented with fluorination systems for hydrocarbons containing HF, HCl, oxygen and a Deacon type catalyst, but no one to date has reported an effective system capable of supporting an efficient oxychlorofluorination reaction. For example, U.S. Pat. No. 3,476,817, issued Nov. 4, 1969, discloses a chlorofluorination reaction in which an aliphatic hydrocarbon is reacted with chlorine in the presence of HF, a Deacon type catalyst, and oxygen in an amount sufficient to improve the catalyst life. However, the oxygen according to this disclosure is not present in an amount sufficient to accomplish an effective Deacon reaction and accordingly an efficient oxychlorofluorination reaction does not take place. U.S. Pat. No. 2,578,913, issued Dec. 18, 1951, discloses the preparation of fluorinated aliphatic hydrocarbons by reacting a hydrocarbon with HF, in the presence of oxygen, a Deacon-type catalyst and a hydrogen halide promoter, such as HCl. However, the hydrogen halide promoter according to the disclosure is not present in an amount sufficient to accomplish efficient chlorination and accordingly an efficient oxychlorofluorination reaction does not take place. In any event none of the above-mentioned patents teach or suggest reactions of aromatic hydrocarbons.
Accordingly, despite the potential advantages of an oxychlorofluorination process, such a process has not been commercialized. To the best of our knowledge, since publication of British Patent 745,818, no attempts have been reported in the literature to make this a viable process for aliphatic hydrocarbons, much less extend it to aromatic hydrocarbons. The reasons for this lack of interest and suspicion of impracticability of the oxychlorofluorination approach are manyfold. As mentioned above, the process as described in British Patent 745,818 cannot be duplicated and cannot be readily adapted for commercially practical results. Further, persons skilled in this art would, in considering commercial feasibility of an oxychlorofluorination process, fear the possibility of explosion and the flammability of hydrocarbons in the oxygen-rich environment present. Also, the likelihood of hydrolysis of the products and/or underchlorinated and underfluorinated hydrocarbon intermediates is imminent since the reactions occur at relatively high temperatures in the presence of water. Another concern would be the possibility of substantial losses of starting materials, underchlorinated and underfluorinated hydrocarbon intermediates and products to combustion. Finally, it, would be expected that the system would be unduly corrosive to known materials of construction due to the combined corrosive active of water, HCl and HF at the elevated temperatures required for the reaction.